Nanoindentation triggers room-temperature recrystallisation in molybdenum

Researchers at the University of Rochester and the Technion–Israel Institute of Technology have found that molybdenum can be recrystallised at room temperature by pressing a diamond tip a few nanometres into its surface. The effect was unexpected: the team had set out to test whether extreme pressure would push the metal into a new solid phase. The work is reported in the Proceedings of the National Academy of Sciences.

An unexpected mechanism

Molybdenum is valued for its heat resistance, melting only above 2,600°C, and is used in nuclear reactors, turbine blades and rocket nozzles. Like other metals, it is made of many small crystal regions called grains. Their size, shape and orientation help determine strength and malleability.

Normally, molybdenum's grains cannot be reformed until the metal is heated to about 1,000°C. Associate professor Niaz Abdolrahim, of Rochester's Department of Mechanical Engineering, said the group had expected a phase transformation under pressure. Instead, they observed a different, stress-driven process.

The role of the pop-in

Using experiments alongside computer modelling, the team worked with a nanoindenter, a calibrated instrument with a diamond tip that is normally used to measure material properties. Even a small applied force produces very high local pressure. At a critical point the tip moves suddenly into the surface, an event known as a pop-in.

Recrystallisation occurs during this pop-in phase, but timing matters. If the test continues well beyond the pop-in, the newly formed grains disappear. Stopping the test manually just after the event leaves recrystallised material in a small region around the indent. The paper's title describes the process as a case of transient instability.

Localised repair without bulk heating

The researchers suggest the method could be used to correct defects within a larger piece of molybdenum, changing the properties of the damaged area while leaving the rest untouched. Afnan Mostafa, a doctoral student in Abdolrahim's group, noted that current repair or regrain processes require heating the whole sample to 1,000°C or more. The new approach instead depends on knowing where to indent, how far to go and when to stop.

Relevance to microchip interconnects

The authors link the work to semiconductor manufacturing. Chipmakers are exploring molybdenum as a replacement for copper in interconnects, the fine wires that join components on a chip. Copper's electrical resistance rises at nanoscale dimensions, which Mostafa said molybdenum avoids.

Molybdenum has its own weakness at room temperature, however: it can fracture with little warning. The team hopes that finding further ways to recrystallise it without heating may improve this behaviour and allow uses that are currently restricted to high-temperature conditions.

Limits and next steps

The source describes recrystallisation only in a tiny zone around a single indent, and the process requires precise manual control of when loading stops. It does not report whether the refined grains improve toughness or how the approach would scale to patterned structures such as interconnects. These remain open questions. The researchers say they plan to explore whether room-temperature recrystallisation can be used to improve the material's room-temperature behaviour, in particular its tendency toward sudden failure.

The study is by Feitao Li and colleagues, DOI: 10.1073/pnas.2612140123.

Source: Accidental discovery enables room-temperature recrystallization of molybdenum (Phys.org, 10 November 2026).

Image: AI-generated illustration.